Phenolic-modified rosins have come into widespread use in vehicles for lithography printing ink, typography printing ink, and gravure printing ink. However, these inks are usually quite costly. In addition, with the development of the printing arts, the speeds of printing have become increasingly high, and requirements for various ink properties such as gloss, drying properties, holdout, film formation, film integrity, reducibility and printability have become increasingly rigorous. Various types of resins have been developed in order to meet these requirements.
For example, in U.S. Pat. No. 2,478,490 issued in August, 1948, there are disclosed rosin-modified, phenol/formaldehyde resins containing rosin esterified by polyhydric alcohols and reinforced by polybasic acids of the maleic type which are useful as printing inks. These rosin-modified phenol/formaldehyde resins and rosin-modified maleic esters are prepared by heating rosin together with phenol/formaldehyde condensates, with maleic-type polybasic acids, or both and subsequently esterifying with polyhydric alcohol in a manner which avoids gelation. This patent goes on to indicate that when the molecular weight of such printing inks is enlarged, they gain considerably in hardness, solubility, chemical resistance and heat stability.
Several methods are disclosed to achieve higher molecular weights. The usual method consists of increasing the amount of phenol formaldehyde condensate, maleic acid-type compound, or polyhydric alcohol, to be combined with the rosin element in the resin. However, both processes and products have definite disadvantages. For example, the procedure is not practical for mass production because gelatinization may occur at an early moment. Further, the products, due to their excessive content of expensive additional compounds, are high in cost, possess low solubility, and contain large percentages of over-polymerized resin particles which render them non-homogeneous.
U.S. Pat. No. 3,896,064 (Koishi, et al) issued on July 22, 1975, discloses vehicles for printing inks containing a resinous component. The resinous component is prepared by the addition reaction of a petroleum resin with at least one unsaturated polybasic acid or anhydride and by subsequent reaction of the resultant product with rosins or rosin-derivatives containing a polyamine to permit quick setting, bring good gloss and provide good stability on printing presses at low-cost. These inks do not contain a phenol/formaldehyde condensation product.
U.S. Pat. No. 4,391,640 (Okoshi, et al) issued on July 5, 1983, relates to a process for producing rosin-modified phenolic resins for printing inks. The process includes reacting a resol-type phenol/formaldehyde initial condensation product, an animal or vegetable oil, a rosin ester obtained by the reaction of rosin with alcohol, and an acid or a hydrocarbon resin. This ink vehicle exhibits excellent gloss and fast set.
There exists a need in the art of gravure printing inks for an ink which is inexpensive and exhibits high holdout, excellent printability and excellent reducibility to allow for a wider variety of gravure applications at lower cost. Further, there is also a need in the art for a more homogeneous printing ink vehicle which exhibits consistent properties.